A Kinetically Stabilized Dianthraceno[2,3-a:3',2'-h]-s-indacene: Stable Kekulé Diradical Polycyclic Hydrocarbon with Triplet Ground State

Abstract

High-spin polycyclic hydrocarbons (PHs) hold significant potential in organic spintronics and organic magnets. However, their synthesis is very challenging due to their extremely high reactivity. Herein, we report the successful synthesis and isolation of a kinetically blocked derivative (1) of dianthraceno[2,3-a:3',2'-h]-s-indacene, which represents a rare persistent triplet diradical of a Kekulé PH. Its triplet ground state was unambiguously confirmed by electron paramagnetic resonance and superconducting quantum interference device measurements. Its structure was also unequivocally confirmed through X-ray crystallographic analysis, and its electronic properties were systematically investigated by both experiments and theoretical calculations. The key design principle is to extend the π-conjugation for achieving the decrease of the bonding interaction and the increase of the exchange interaction between unpaired electrons, which are essential for accessing the stable triplet ground state. Due to kinetic blocking, 1 shows a reasonable stability with a half-life time of 64 h under ambient conditions. It has a narrow HOMO–LUMO energy gap and displays amphoteric redox behavior. Notably, its dication and dianion exhibit a closed-shell ground state and near-infrared absorption, and the structures were identified by X-ray crystallographic analysis. This study will shed new light on the design and synthesis of novel stable PHs with high-spin multiplicity.